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The deadly attack on a Christchurch prostitute, repeatedly run over by a car as she pleaded for her life, "couldn't get much worse", a judge says.

Peter Steven Waihape, 29, was yesterday sentenced to the open-ended jail term of preventive detention, on top of life imprisonment with a non-parole period of 18 years, for the rape and killing of the 24-year-old woman last December.

He was also sentenced to a total of 10 years' imprisonment for the abduction and sexual violation of a teenager just three days before the killing.

In the period between the two attacks, Waihape approached Christchurch mental health providers and spoke about what he had done, raising speculation that the killing could have been prevented.

But Justice Lester Chisholm said yesterday: "The information I have read does not lead me to the conclusion that any professional should bear responsibility for the shocking events that were to follow".

The victim of the earlier attack by Waihape yesterday spoke of how news of the killing had left her numb and questioning what more she could have done to prevent it.

Waihape had abducted her from the street in his car, bound her hands in the same way as the prostitute, before violating her and dropping her off.

"I can't look at myself any more. I feel detached from my body," she said.

The High Court in Christchurch heard the full grisly details of the killing yesterday.

Waihape picked up the prostitute for sex and drove her to a carpark, where a dispute broke out about him not using a condom.

He partially strangled her, removed her clothing, bound her hands and raped her. He then pushed her out of the car and ran over her. She became trapped under the car and was pleading for her life.

"Rather than listen to her pleas, you ran over her again," the judge told Waihape.

Witnesses reported hearing him laugh as he did so.

"You were then seen to get out of your car and kick her at least twice. She managed to free herself and sat up. She pleaded for her life. Then you drove at her a number of times, smashing through a concrete wall."

Waihape later drove her to the river and threw her half-naked body into the water.

"The ultimate indignity was that you used her as a stepping platform to get out of the river. It couldn't get much worse, Mr Waihape."

A witness to the attack said she had been forced to move out of her house because of "recurring flashbacks and nightmares", and she was even considering leaving the country.

"I constantly live in fear that someone who knows [Waihape] may come after me. I was constantly asked why I didn't help [the victim]. It was gut-wrenching to hear."

The murdered woman's mother told the court she was proud of her daughter for battling to beat drug addiction as she tried to raise a young daughter of her own. "We are left with the responsibility of raising our granddaughter the best we possibly can. In caring for her needs, we can never replace a mother's love for a child."

The dead woman's father described becoming deeply upset at watching his granddaughter stand next to his daughter's coffin and rubbing her stomach.

"When I left [she] wanted to come home with me to see her mum."

The mother said Waihape was a "calculated, cold-blooded murderer, who does not deserve to live".

Waihape's lawyer, Leuatea Iosefa, said Waihape was remorseful and had tried unsuccessfully to seek psychiatric help prior to the killing.

Waihape had claimed he had felt like he was killing his mother, rather than the prostitute.

Justice Chisholm said Waihape clearly had come from a dysfunctional family and suffered from depression and mood disorders.

But he had had "numerous opportunities" to deal with issues he had been facing.

"It is dangerous to speculate you will not offend again in the future."